Signal Processing Toolbox

Special Topics in IIR Filter Design

The classic IIR filter design technique includes the following steps.

1. Find an analog lowpass filter with cutoff frequency of 1 and translate this "prototype" filter to the desired band configuration
2. Transform the filter to the digital domain.
3. Discretize the filter.

The toolbox provides functions for each of these steps.

Design Task	Available functions
Analog lowpass prototype	buttap, cheb1ap, besselap, ellipap, cheb2ap
Frequency transformation	lp2lp, lp2hp, lp2bp, lp2bs
Discretization	bilinear, impinvar

Alternatively, the butter, cheby1, cheb2ord, ellip, and besself functions perform all steps of the filter design and the buttord, cheb1ord, cheb2ord, and ellipord functions provide minimum order computation for IIR filters. These functions are sufficient for many design problems, and the lower level functions are generally not needed. But if you do have an application where you need to transform the band edges of an analog filter, or discretize a rational transfer function, this section describes the tools with which to do so.

Arbitrary-Response Filter Design

Analog Prototype Design

© 1994-2005 The MathWorks, Inc.